Art of oxidizing ammonia.



L. 0.1J0Ns, D. A. MoRToN '& G'. N. TBRZIEV.

ABT 0F OXIDIZING AMMONIA.

APYLIUATIDH FILED AUG. E, 1911.

rammed sept. 3i 1912-.

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UNITED sTATEs lPATENT oEEIoE.

LOUIS C. JONES, DARWIN A. MORTON, AND GrEOEtGrE.V N. TEEBZIEV, F SYBACUSE, NEW YORK, ASSIGNOBS TO SEMET-SOLVAY COMPANY, OF SYRACUSE, NEW YORK, A

CORPORATION OF PENNSYLVANIA.

Amr or oxrnrz-ING AMMONIA.

Specification oiiLetters Patent. i Patented s e-ph, 1912.

Application led August-5, 1911. Serial No. 642,573. g

To ZZ 'azhom z't may concern:

Beit known that we, LOUIS C. JONES,

- DARWIN A. MoRToN, and GEORGE N. TERzIEv,

citizens of the United States, residing at Syracuse, in the county of Onondaga and State ofNew York, have invented Vcertain new and useful Improvements in the Art of (')xidizing Ammonia, ofwhich the following is a specification.

Our invention relates to the formation of oxids of nitrogen by the catalytic oxidation of'ammonia to the end of producing nitric acid.

It .is well known thatwhen ammonia ga's in company with oxygen is submitted to catalytic action oxids of nitrogen may be produced. Heretofore various catalytic agents have beentried for this purpose and ing a mixture of ammonia gas and oxygen through this in the proportion of one volume of NH, gas to two volumes of oxygen and at a temperature of from 7 00.OA C. to

750 C., not onlyisl a practically complete oxidation .of the nitrogen of the ammonia into nitrogen oxids,capable of conversion into nitric acid, effected, but the compounds formed are ,not subject to decomposition after their formation. l

The catalytic agent employed by us to effect the reaction is a plumbate, i. c., a compound of lead oxid with the oxid of another suitable metal or base. The base, the oxid of which is combined with the oxid A.of lead, must be of such naturetliat its `oziidhas no .tendency to revert, atfthe temperature of the reaction, to its-hydroxid'or carbonate 1n the presence of water vapor or CO2. Y Furthermore, it must form with lead oxid a plumbate which is infusible within the range. of temperature at which the conversion of NH3 to oxids of nitrogen is most complete. 'For example, the metals magnesium, zinc, aluminum, and cadmium conforn tothis defini tion. The compound may be made by heat-v ing together either the oxids themselves or the hydroxids, carbonates, nitrates, or other compounds of the metals employed which at a temperature of or below red heat easily yield the oxids. Thus specifically we may produce a plumbateV desirable for our purpose by mixing lead oxid with its molecularl equivalent of magnesia and heating the mixture to a temperature of about 800 C. for from four to six hours, with frequent stirring to insure excess of oxygen from the air. The lumpy mass formed 1s, after cooling,

broken into small pieces and placed in the apparatus through which the ammonia andair mixture is to be passed. y v 0 Such an apparatus is illustratedin section 1n Figure -1 of the drawings. ',Fig. 2 shows a diagrammatic view of means for forming and regulating the mixture of ammonia and `air employed.

The apparatus, as shown in Fig. l, consists of a shell, A, forming a hollow vessel within which is contained the catalytic material, B, which latter may be held in place by perforated plates of silver, or other nonoxidizable metal a, a. The shell, A, consists of a non-oxidizable metal, or in case it consists of a base metal, should be lined with a non-oxidizable metal, such as silver, or other material which will prevent the gases from coming in contact therewith. We `have found it convenient to make the shell, A,V of iron, protecting the inner surface by a lining of asbestos, C, and packing upon the asbestos a dense layer, c,\of the catalytic material, so as to'prevent the mixed gases fromy coming in contact with the iron container, or, in case they do, only at a com aratively low temperature. `This precaution is necessary in view of the fact that ammonia gas mixed with oxygen, if heated to a vtemperature of about 700 C. in contact with many substances, particularly iron, is only 0x1- dized to the extent 'of producing water vapor from the hydrogen present, leaving the nitrogen free, in which condition no further oxidation can take place.

For the saine reason the iron surface of the approach to the catalyzer, which may otherwise become considerably heated, should be protected from contactwith the gases, a's shown at D, and the catalytic substance itself must be free from certain impurfties, particularly oxid of iron. The

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,e tion can be used in part Vfor other useful llating material and ther external cooling be more than ten per cent. `in excess of this.

passing atmospheric air through .ammonia completely oxidize 'NH3 or by decomposition and temperature of the gases entering the periment 1n any given case. The tempera- 'ing out of the products of combustion by.`

, In Fig. 2 of the drawings we have illusL layer of asbestos and the compacted layer of contact. material, both of which serve' as insulators,eprevent the heat developed by the reaction witliin the apparatus `from reaching the outer wall in sufficient amount to heat it to a temperature high enough'to produce injurious eiects, even if the gases should reach it. By this arrangement also, the heat of the reaction is conserved tosuchv an extent thatlittle or no external yheat is required'l to sustain the required temperature, which, to produce the best results, .shouldralnge between 700 C. and 750 C.. It is, therefore, ordinarily unnecessary to use a recuperating system' to preheat the gases and the heat produced by the reacwork. In case, however, the apparatus is small and radiation proportionately great, recuperation may be resorted to tomaint-ain the temperature at the required point. Care must, however, be taken to prevent the heatv produced by the reaction from raising t e .temperature above 7 50o C., the maximum at which satisfactory yields are obtained, since above this temperature, with the theowill be developed eitherv through failure to of the'oxids formed.' v t The temperature may be controlledby providing a proper adjustment of the insuto correspond withv the amount, dilution,

apparatus2 as may be ascertained byV exture mayalso be reduced by reducing ther proportion of NH3 in the gas mixture. In this case oxidation of NH3-will be e'qually complete but there will be a waste of energy through the introduction of excees of air.

'In conducting the' operation the contact material is first brought to a temperature suiiiciently high to start the reaction by directing' a flame against onepf the perforated plates, aa. The ammonia gas with air in Vproper-proportions to provide an excess of oxygen is then introduced and the reaction begins immediatelyupon the sweep' the air and ammonia mixturei' The proportion of oxygen to lammon should not be less than two volumes of o gen to one volume of proportion, of oxygen m creased somewhat, but shou v Y ndl preferably not l A mixture of ammonia gas and oxygen pf proper proportions may be obtained by liquor having Ya strength -of from S-t -80 per liter, NH3 at a temperat trated means byvwhich this fact may be utilized in providing a continuous supply of the gas mixture of proper proportions. In this, l indicates a vessel, such as the absorber of an ammonia still, containing ammonia liquorof high strength, e. g., 200 grams per' liter, or over. From this the ammonia liquor iiows by pipe, p, provided with aregulating valve, QJ, to a vessel, or tank, 2, at such a rate as to maintain the solution therein at theAstrength requisite to give a mixture of the desired proportions, when air is passed through it. The overliow from vessel, 2, passes by pipe, p', to vessel, or tank, 3, and thence by pi e, p2, to a fourth vessel, 4. Air is forced iist through'the liquor intank, 4, and thence through tanks, 3 and 2, on the counter current principle and from tank, 2, to the catalyzer. The impoverished liquor from tank, 4, is pumped back to the absorber, 1, to be thereinrecon'- centrated.' It will be understood that. the rate of iow from the absorber, l, to vessel,

2, will be so proportioned to the amount of` air passin through vessel, 2, as to'm'aintaink constant is, in our process, converted into oxids in the formv N203, or approximating N203, which may, after cooling, be absorbed and Voxidized in towers to producev nitric acid.

At the temperature described there is little or no tendency for the oxids of nitroo'en, when once formed, to be broken up by urother contact with the catalytic agent employed. Hence it is not essential that the gases' shall pass vthe contact agent at any specific speed to bringvabout ythe desired result, except that it is economical to pass the gas as rapidly as possible and still have the ammonia completely oxidized. Any'slower speeld, however, does not materially decreasethe amount of oxids of nitro en produced per unit of ammonia consume What we claim asnew and desire to se-A cure b Letters Patent, is:

1. T e hereinbefore describedprocess of vproducing nitrogen oxids which consists in passing ammonia gas with an excess of'oxy-V gen in contact with a catalytic agentconsistingldof a plumbate at a temperature below t at atwhich the oxids of nitrogen formed begin to decompose."

2. Thehereinbefore described process of produ nitrogen oxids which \.consists in passig'alnmonia gas With-an excess of oxygen contact witha catalytic agent consisting' of a plumbate at a temperature vof from 7000356', to 750 C.

3. The'ffrliereinbefore described process of Vproducing nitrogen oxids which consists in passing 'ammonia gas with an excess of oxysubscribed our names; this 1st day of 10 gen in Contact with a catalytic agent con- August A..D., 1911. l sistng of a plumbate formed from the oxds of leed and of a metal the oXd of which, at- LOUIS C JONE' a temperature vof 750o C., is infusible and DARVVIN A' MORTON has no tendency to revert to its .hydroxd or i carbonate in the presence of Water vapor `Witnessesz or C02. HORACE Gr. CARRELL, In testunony whereof, We have hereunto H. DUANE BRUCE.

GEORGE N, TEEZIEV. 

